Peering into the dark

By Dr Dave Pearton

The diving at Sodwana Bay is justly regarded as some of the best in the world, but it also ranks as some of the most challenging, with “exciting” beach launches through the waves that raise the adrenaline of tourists more used to calm tropical lagoons.  This is doubly the case when the sun sets and a diver’s world is reduced to the small beam of light from a torch with the knowledge that things (potentially with sharp teeth) wait, unseen, in the darkness. This, and the variable weather, makes it difficult to study phenomena that occur exclusively at night, such as the annual mass coral spawning taking place each summer.

ORI scientists and students, led by Dr David Pearton and Dr Michael Schleyer, travelled to Sodwana after the full moon in February as part of a research project to learn more about this critical process. The annual spawning ensures that new coral recruits are available to maintain the health and resilience of the reefs, both in Sodwana as well as, potentially, all along the KZN coast. The weather this season, unfortunately, put paid to any night dives that would allow direct observation of spawning activity. Fortunately, there are indirect ways of looking at these phenomena. Improvements in gene sequencing technology have opened up new methods of determining the identity and timing of which species are spawning by looking for the microscopic eggs and larvae hidden in the plankton above the reef using genetic metabarcoding. To do this, plankton tows were conducted each morning and these will subsequently genetically sequenced en masse, and powerful computer algorithms and databases will enable us to detect and identify the few coral larvae present in the tens of thousands of other organisms that make up the plankton.

During the trip the ORI scientists were also able to work on several other projects, including conducting the annual monitoring of corals at Nine Mile Reef.  This is one of the longest continuous coral reef monitoring projects of its kind in the world and has contributed immensely to our knowledge of reef dynamics and the threats they face.  They were also able to service a whole suite of instruments including temperature recorders and Acoustic Doppler Current Profilers (ADCPs) as part of the CAPTOR programme. These instruments give a detailed picture of the currents over the reefs which is essential in order to be able to model and predict where the various larvae from corals, fish and other organisms will be distributed. This is vital information to assist in the design and management of our MPAs.